Disable Blender autosaving files
Are you talking about auto save or do you mean that when Blender opens up it automatically opens your last saved project?

Anyway go to File Menu > User Preferences > File Tab > Auto Save: on the bottom right

Disable either Auto Save Temporary Files, reduce the number of files, or disable Keep session if when Blender opens up for the first time it automatically brings up the last opened file.

Keep session doesn't really save the changes to you actual work file however, as far as I know the session is saved to an internal Blender file in the user folder in the last state it was before closing. The actual work file in its directory however should be unchanged and hold only the changes up until the last explicit user save.

Beware that some addons do an automatic save of the file on export (like Blend4Web for example) even if you don't save the file, on export it automatically saves any changes without warning the user or specific user consent, resulting in unwanted and unforeseen file saves. If you are using any addons check in it's preferences if there is such setting as 'auto-save'